Covid vaccine increased menstrual bleeding in 42% of women

The largest study to date with over 35,000 attendees -women and people of gender diversity- confirmed that 42% of women experienced increased bleeding from the menstruation Within two weeks of vaccination against covid.

In addition, the study describes for the first time the occurrence of spontaneous bleeding in a high number of people who did not have periods -because they were menopausal or because they were undergoing hormonal contraceptive treatment or for a sex change-, after having received the vaccine against SARS-CoV-2.

The conclusions of this study, published this Friday in the journal Science Advances, confirm a side effect reported by women and ignored by Science and reveal that this effect of the vaccine affected “a significant number of people”.

However, the study data show that these alterations are temporary and are associated with certain triggering factors such as age, suffering from systemic side effects related to the vaccine (fever or fatigue), or a history of pregnancy and childbirth. , among others.

“Menstruating and menstruating people began to report unexpected bleeding after receiving the vaccine in early 2021,” said US study researchers and leaders Katharine Lee of Tulane University and Kathryn Clancy of the University. University of Illinois at Urbana-Champaign.

An ignorant side effect

In the trials of vaccines she is usually not asked about menstrual cycles or bleeding, so this side effect is often overlooked or excluded from studies, despite the fact that some vaccines, such as typhoid, hepatitis B, and HPV, can alter menstruation.

To do the study, the authors used a survey asking people about their experiences after receiving the covid vaccine.

The authors only included data from the people who had not passed the covid (because the disease can cause menstrual changes) and excluded data from people aged 45-55 to avoid confusing the results with menopause or earlier changes.

Thus, the study focused on menstruating people, postmenopausal women and people on hormone therapies that suppress the cycle.

42.1% of respondents said they had heavier menstrual flow in the first two weeks after vaccination, 43.6% that their menstrual flow had not changed and 14.3% had experienced no change or , if any, less bleeding than usual.

The study detected possible associations with reproductive history, hormonal status, demographics and changes in a person’s menstruation after vaccination.

For example, respondents who had spent a pregnancy were most likely to report heavier bleeding after vaccination, with a slight increase in those who had not given birth.


And over 70% of respondents who used contraceptives long-acting reversible hormones and 38.5% of those taking gender-affirming hormone treatments reported this side effect.

Although menstrual disorders are not uncommon or dangerous, unexpected changes can be concerning.

“Unexpected intermittent bleeding is one of the first signs of certain cancers in people who are postmenopausal and those who use gender-affirming hormones,” says Lee.

This is why “this screening is very important in order to be able to detect cancers in time”, explains Clancy.

The authors reiterate, however, that getting vaccinated is one of the best ways to prevent covid, hospitalization and death.

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